Cellular analysis by flow cytometry has reached a high level of both sophistication and parallelism, enabling its widespread use in life science research and medical diagnostics alike. Yet for all its remarkable success as a technology, much remains to be done in order to meet significant needs in terms of applications.
One of the areas where flow cytometry has not yet made significant inroads, but could potentially bring tremendous benefit, is the analysis of very rare events. The diagnostic/prognostic fields of Circulating Tumor Cells (CTCs) and detection of fetal cells in maternal blood are well-known examples of what could be called ultra-rare-event analysis; here the “interesting” cells make up a minute fraction of the total cells in the sample. For example, out of the ˜109 cell/mL concentration of normal cells in blood, CTCs with clinical significance can range from 105 to less than 1 cell/mL. Additionally, current technology based on surface-antigen binding (whether magnetically mediated or not) will, by design, miss cell populations not defined by surface antigens. Missing relevant cells is particularly serious in CTC analysis, where false negatives can, at best, reduce assay effectiveness, and at worst, contribute to higher patient mortality. Since flow cytometry is not restricted to surface-antigen recognition, but can additionally identify cells based on intracellular markers (e.g., vimentin or cytokeratin, for mesenchymal cells), nucleic-acid content, and even morphology, it could come to the rescue; that it has largely not, so far, is an indictment of its current limitations in terms of volumetric sample delivery and analytical throughput with regards to rare-event analysis.
If one were able to break through the current technology limitations in flow cytometry and deliver drastically improved volumetric throughput (“extreme throughput”), a number of benefits would result. In the example of rare-event analysis for CTCs, one could envision executing a protocol in minutes instead of hours or even days, significantly reducing the costs of diagnosis and monitoring; more importantly, testing simply not done today would all of a sudden become practical (and affordable) to execute. This innovation would radically simplify existing workflow by allowing the rapid, routine analysis of patient specimens, avoiding the majority of the complex sample preparation steps involved in current practice. Additionally, there would be more transformational changes involved in applying the proposed approach to rare-event analysis than just boosting throughput to extreme levels (in itself sufficient motivation). By bringing the analysis rate of flow cytometry up to the level of immunocapture-based technologies for CTC applications, one would not simply add another analytical modality to the mix: one would leverage five decades of platform and assay development. Flow cytometry has shown a remarkable ability to adapt over time to evolving scientific findings: As new markers emerge, as new cellular identification strategies are identified and developed, flow-based protocols have been quick to incorporate the new possibilities into the technology and the discipline. The result is a stunningly flexible set of tools that can be used to count, identify, analyze, characterize, select, and (by sorting) harvest and purify desired cells in a mix. Bringing this toolset to bear in the emerging field of CTC analysis would present tremendous opportunities to researchers and, ultimately, clinicians in their efforts to understand, control, and fight cancer. Specifically, an extreme throughput analyzer would allow CTC detection (and ultimately, capture) based on multiple selection criteria, criteria updateable over time, and would do so faster, more reliably, and with simpler sample preparation than with currently available technologies. Ultimately, it is expected that such an analyzer, by returning more accurate results and providing an earlier, more sensitive detection of the metastatic process, could help to significantly improve the survival odds of cancer patients.
More broadly, the development of an extreme-throughput flow cytometry technology platform relying on familiar, established assay and protocol formats would make the tool attractive not only for research laboratories, but also in the context of High-Throughput Screening (HTS) for pharmaceutical development, as well as in clinical environments performing generally routine flow-based tests-again, by drastically speeding up performance, by simplifying the sample preparation procedure, and by delivering improved sensitivity.